With the rapid progress of nano scientific technology, demands on nano-scaled material are increasing and the size of an electronic device is more and more decreasing. Thus, photolithography, which is the existing top-down approach used to manufacture a silicon device, is reaching the limit. Namely, although currently used photolithography technology for manufacturing a silicon semiconductor has many advantages in terms of process optimization and applications, it is difficult to fabricate a printed circuit of 30 nm or less due to technical limitations of dispersion of light and wavelength of the light source. In addition, studies on electron beam lithography or EUV (extreme ultraviolet) lithography are under progress. However, the former is difficult to simultaneously form two-dimensional patterns, and the latter has difficulty in controlling light absorbed in photoresist or lifespan of an optical instrument because significantly high optical energy should be used.
Therefore, to develop next generation semiconductor, problems of the existing photolithography technology should be overcome, and it is also required to reduce manufacture cost and simplify the process. Recently, as a method satisfying these requirements, self-assembly method of a block copolymer is being studied. A method of forming patterns using a nano structure of a block copolymer, unlike the existing methods, has advantages of simultaneously forming two-dimensional patterns. Particularly, a nanostructure is simply formed by microphase separation between the chains of a block copolymer, and thus, a process cost may be reduced.
A block copolymer includes polymer blocks having different chemical structures, connected through a covalent bond, and according to the compositions of blocks constituting the block copolymer, the length of the chain, and Flory-Huggins parameter, it may form various nano structures including a complicated three-dimensional structure such as a gyroid, or a HPL (hexagonal perforated lamellae) structure, as well as a basic structure such as a sphere, a cylinder, or a lamellae. And, the size of the nanostructure may be controlled from 5 to 50 nm, according to chemical structure of a block copolymer, compositional ratio of blocks, or molecular weight, and the like. Lithography using a block copolymer (pattern forming method) refers to transcribing a nano structure of the thin film of a block copolymer onto a substrate to form nano patterns. The cost is significantly low, and the manufacturing process may be very simple, compared to photolithography currently used in a semiconductor manufacturing process.
Meanwhile, with the progress of polymer synthesis technology, studies on chemical physical factors influencing on the synthesis and nano structures of various block copolymers have been widely progressed. Particularly, studies on the control of a nanostrucrue using a PS-PMMA (polystyrene-polymethacrylate)-based amorphous block copolymer have been intensively progressed. Namely, if morphology of a PS-PMMA block copolymer is controlled by microphase separation, a cylindrical nanostructure arranged in a hexagonal shape may be easily formed. However, since the cylindrical nanostructure arranged in a hexagonal shape is inappropriate for use in a microcircuit printing process in the semiconductor industry, it takes more time to manufacture related electronic devices and energy consumption is high.
Accordingly, from an economical point of view, and considering semiconductor circuit design and software, a cylindrical nanostructure arranged in a square (or rectangular) shape is much more favorable than a cylindrical nanostructure arranged in a hexagonal shape for manufacturing an electronic device. On this account, recently, studies on formation of a cylindrical nanostructure arranged in a square (or rectangular) shape by self-assembly or microphase separation of a block copolymer are actively progressed. For example, it was reported that a PS-PMMA diblock copolymer is coated on a substrate having chemical patterns of a square (or rectangular) arrangement, and then, formation of a nanostructure with a square (or rectangular) arrangement is forcibly induced. However, there is a problem that a nanostructure arranged in a square shape may not be formed unless the cycle of the chemical patterns and the cycle of the nanostructure of the block copolymer coincide with each other.
Meanwhile, it was reported that if an A-B-C type triblock copolymer having three blocks is used instead of the above explained diblock copolymer, a nanostructure arranged in a square shape may be formed in a narrow area. And, it was also reported that using a triblock copolymer having a core-shell spherical nanostructure, a nanostructure of a square arrangement is formed only on the uppermost layer according to the thickness of the film. And, an inorganic block with high etching resistance was introduced in a triblock copolymer to embody a cylindrical nanostructure of a square arrangement, which could not be obtained with a diblock copolymer, thus suggesting applicability as a next generation nano patterning technology.
However, examining the above explained study results, to form a cylindrical nanostructure arranged in a square (or rectangular) shape, which is suitable for a semiconductor circuit design, it is required to separately use a photomask having micrometer-scaled topological or chemical patterns together with a diblock copolymer, which is a substrate for forming a nanostructure, or to prepare and use an A-B-C type triblock copolymer that is difficult to synthesize due to its complicated molecular structure, or to additionally use an additive inducing a nanostructure or a mixture causing a hydrogen bond between molecules. On this account, these are too complicated to apply as a next generation nano patterning technology or economically infeasible. Furthermore, the existing PS-PMMA diblock copolymer that has been intensively studied so far as well as any kinds of diblock copolymers could not directly form a cylindrical nano structure arranged in a square (or rectangular) shape without an auxiliary material or additive having a nanostructure transcribed thereto.
Namely, according to the prior art, a cylindrical nano structure arranged in a square (or rectangular) shape could not be formed, or separate use of a phosomask was required or synthesis of the block copolymer itself was complicated. On this account, any pattern forming method using previously known block copolymers may not easily form a nano structure arranged in a square (or rectangular) shape, and thus may not be suitably applied for design and mass production of semiconductor circuit.